The upstream flange plate of a fan rotor is generally removable so as to enable a blade to be replaced in the event of damage. This can occur in the event of foreign bodies, such as birds, being ingested, in particular during the takeoff and approach stages of an aircraft fitted with turbojets.
For assembly reasons, axial clearance is included in the connection between a blade and the disks. The random axial position of a fan blade within this clearance unbalances the rotor and generates vibration in operation. This is particularly true for fan blades that are of large chord.
The large centrifugal forces to which blades are subjected in operation can also lead to blades being moved axially in random manner within said assembly clearance.
U.S. Pat. No. 4,033,705 discloses a system for retaining blades axially, which system comprises, at each end of a blade root, a tenon which co-operates with two oblique mortises arranged in the rim of the disk on either side of the groove receiving the blade root. The tenons provided on each face of the disk are held radially by a ring secured to the disk. Between each end face of the blade root and the adjacent tenon, that document provides for spring-forming sheet metal acting to prevent the tenon from moving radially while the blades are being assembled, prior to the retaining ring being put into place and fastened. Those springs create assembly clearance at each end of a blade, as can be seen in FIG. 7 of that document, which clearance is not under control.
U.S. Pat. No. 5,282,720 provides for interposing honeycomb elements between the retaining flange plates and the ends of the blade roots, the honeycomb elements serving to absorb a portion of the energy in the event of birds being ingested. During ingestion, the honeycomb deforms progressively, thereby dissipating a portion of the energy. The honeycomb elements must retain their integrity during assembly of the flange plates, and as a result there inevitably exists some axial clearance after assembly, thereby making random axial displacement possible while the fan is in operation.